NewExpression

NewExpression is a term used in programming language theory and documentation to describe an expression that creates a new instance of a class, struct, or array. In most compiled languages it corresponds to the syntax that allocates storage on the heap and initializes the object, while in dynamically typed languages it also controls prototype inheritance. The name stems from the keyword “new,” which appears in languages such as Java, C#, JavaScript and Swift.

In Java the syntax is new ClassName(constructorArguments), where the class constructor is invoked and the reference to the allocated object is returned. Arrays use new int[10] to allocate a contiguous block of primitive values. JavaScript follows a similar form, new Constructor(params), but the expression creates an object with Constructor’s prototype as its internal prototype chain and returns the newly created object unless the constructor explicitly returns a different object. C# follows the same pattern, but its new expression can also be applied to value types, producing a default instance that is allocated on the stack or inlined in objects.

From a memory management perspective a NewExpression typically allocates on the heap, making it subject to garbage collection or manual deallocation depending on the runtime. Some languages provide deterministic finalization (C++ new/delete, C# IDisposable), while others employ automatic garbage collection (Java, JavaScript, Swift). The allocated object may be a reference type, a boxed primitive, or an array, and the actual size depends on the type definition and arguments.

Common pitfalls include omitted parentheses in languages that allow default constructors, unintentionally returning primitive values instead of objects in JavaScript, and overuse of new inside tight loops which may lead to frequent garbage collection pauses. Best practices recommend reusing objects when possible, employing object pools, and using language‑specific constructs such as Java’s try‑with‑resources or Swift’s defer to ensure proper cleanup.